1. Field of the Invention
The present invention relates to a radiographic image detector, a radiographic imaging apparatus and a radiographic imaging system. The present invention particularly relates to a radiographic image detector, radiographic imaging apparatus and a radiographic imaging system for direct conversion of radiation into charges.
2. Description of the Related Art
Many radiographic image detection apparatuses recently being put into practice employ radiation detectors such as Flat Panel Detectors (FPDs) that have a X-ray-sensitive layer disposed above a Thin Film Transistor (TFT) active matrix substrate, and are capable of directly converting X-ray data into digital data. Such FPDs have the advantage of enabling more immediate image and video image confirmation than for example conventional film screens, and their use is rapidly widening. Various types of these radiation detectors are proposed. For example, direct-conversion-type in which radiation is directly converted into charges in a semiconductor layer and the charges accumulated, and indirect-conversion-type in which radiation is first converted into light by a scintillator, such as CsI: Tl or GOS (Gd2O2S:Tb), and then the converted light is converted into charges in a semiconductor layer and the charges accumulated, are proposed.
In radiation detectors, for example, plural scan lines and plural signal lines are disposed intersecting with each other, and pixels are disposed in a matrix pattern corresponding to each of the intersections between the scan lines and the signal lines. The plural scan lines and the plural signal lines are connected to an external circuit peripheral to the radiation detector, for example an amplifier Integrated Circuit (IC) or a gate IC.
Reducing the size of the pixels in radiation detectors is an effective way to increase the resolution of FPDs. Particularly, in direct-conversion-type radiation detectors employing, for example, Se, various radiation detectors are proposed for high definition enhanced image quality that contribute to increasing the resolution whilst leaving the pixel size virtually unchanged. For example, products with small pixel size are proposed for FPDs for mammography where there is an emphasis on resolution.
The use of hexagonal shaped pixels in radiation detection apparatuses in order to achieve an increase in both resolution and sensitivity, is proposed (see for example Japanese Patent Application Laid-Open (JP-A) No. 2003-255049), since simply reducing the pixel size may lead to a drop in sensitivity due to the proportional relationship to surface area in a radiation detection element. With square shaped pixels, the resolution in diagonal directions is lower than in the horizontal and vertical directions. However, employing hexagonal shaped pixels may secure high resolution in each of the horizontal, vertical and diagonal directions.
When still imaging and video imaging (fluoroscopic imaging) by using the hexagonal shaped pixels described above, methods of reading charges from plural pixels at the same time and summing the obtained values (binning) shall be considered, in particular in order to maintain a high frame rate such as in video. Performing such pixel summing within a sensor must also be considered.
However, in pixel summing of plural hexagonal shaped pixels, unevenness in pixel positions (the positions of the center of gravity when plural pixels are treated as one pixel cluster) may occur before and after summing, depending on the summing method. Accordingly, even resolution in each of the horizontal, vertical and diagonal directions that has been secured in before summing secure may not be maintained in after summing.